Production by spinning of cellulose hydrate filaments



United States Patent PRODUCTION BY SPINNING OF CELLULOSE HYDRATEFILAMENTS Martin Studer and Louis Willimann, Emmenbrucke, near Lucerne,Switzerland, assiguors to Societe de la Viscose Suisse, Emmeubrucke,near Lucerne, Switzerland, :1 Swiss body corporate.

No Drawing. Application July 28, 1952, Serial No. 301,364

Claims priority, application Great Britain July 31, 1951 Claims. (CI.18-54) The present invention relates to a spinning process for theproduction of filaments of all kinds from viscous solutions which arecharacterised by a highly oriented crystalline structure and inconsequence a high tensile strength, and to the filaments so obtained.The term filaments as used herein is to be understood to. cover multipleand single filaments, fibres, small ribbons and foils.

It is possible to produce viscose filaments having a relatively highstretching capacity and tensile strength up to about 3.5 g./den. in thedry condition and about 2.0 g./den. in the wet condition. This isfrequently achieved by softening and simultaneously stretching thefreshlyspun thread in one or more baths at temperatures which may be,for example, higher than 70 C. Other processes employ spinning bathswhich either have a high content of, zinc sulphate or have, a minimalcoagulating action on the viscose solution. The object of all theseprocesses is to make it possible to subject the thread to a high degreeof stretching during the spinning, operation itself or immediately afterthat operation. However, there is 111 practice a limit. to the amount ofstretch that can. be eftected since the filaments, due to frequentbreakage, cannot be stretched beyond a critical tension without damageor loss of quality. By increasing the stretch eifected during spinning,an improvement in the crystalline structure and the orientation of themacromolecules can be efiected but it has not hitherto been possiblewith any viscose process, because of frequent interruptions due tobr'eakages, to exceed a stretch of about 150%. On the other hand,filaments of. cellulose acetate can be stretched and simultaneouslysaponified to cellulose to yield filaments of well developed.crystalline structure and good orientation. It is possible that avstretching action with simultaneous saponifica-tion of ester groupsassists the crystallization of the cellulose and the orientation of themicelles or crystallites.

According to the present invention a processv for the production offilaments of high stretching capacity and high tensile strengthcomprises spinning through spinnerets a viscose of gamma number above 60in such a manner that the degree ofpolymerisation of the filament isabove 300 into a spinning bath of low electrolyte content andstretchingthe filaments continuously with their formation, the spinningbeing effected at room temperature and the stretching of the filamentsbeing effected so that the speed of travel of the filaments afiter suchstretching is not greater than 12 metres/ minute.

The gamma number is the number of mols of CS2 combined per glucoseradical multiplied by 100. Viscose solutions of gamma number above 60may have a cellulose content of about 4 to 11% by weight and a causticsoda con-tent of about 3 to 12% by weight, that is to say, they are ofnormal composition. Wood pulp or linters or othervcellulose productsemployed in the viscose industry are used as cellulose-containingstarting materials. The production of the viscose solutions is eifectedin the usual manner. Cellulose xanthate containing cellulose of highmolecular weight is particularly useful and is obtained by treating amaterial containing cellulose of high molecular weight with caustic sodaand omitting the ripening of the alkali cellulose. The average degreesof polymerisation of the cellulose hydrate regenerated from the alkalicellulose or the viscose are, in accordance with this invention, above300. 7

These viscose solutions are spun into baths which have a weakcoagulating action, a low sulphuric acid content and a relatively lowelectrolyte content and which are operated at room temperature, by whichis meant about 10 to 25 C. The sodium sulphate concentration ispreferably kept below 100 g./lt. Such metal salts as Zinc sulphate, ironsulphate, aluminium. sulphate and magnesium sulphate which tend toreduce the stretchability of the filament are avoided. The sulphuricacid concentr ation is preferably 1 0 to 40 g./lt. Substances such aslau'ryl pyridium chloride or sulphate, which facilitate spinning may beadded to the spinning bath. Whenv viscose solutions having relativelyhigh gamma numbers are spun into such baths, filaments are produced.which are clearly different from those which are spun from the so-calledMiiller baths (containing 10-14% H2804 20-25% NazSOr, 0.5-2.0% ZnSO4;operated at temperatures 4050 C.). The products have an almost circularcross-section and although this is not specific solely for theconditions of the, present process, there is no indication in thepresent products of the so-called double layer that can easily beobserved, using, the phase-contrast microscope, in viscose fibrecross-sections made. with Miiller baths and subsequently coloured. Onthe other hand very small dots are revealed by microscopic examinationof the fibre cross-section and these probably correspond to micropores.The filaments obtained may be stretched, in, accordance with theinvention by more than 1.50% and preferably. 200% to 400% if individualfilaments of less. than 10 denier are required. For the production. ofsingle filaments, or small ribbons or the like above 10 denier, thestretch must be reduced.

It has surprisingly been found, and this is a characteristic feature ofthe present invention, that these high speed is employed. The speed ofthe filaments after the, stretching operation is, less than 12 metresper minute and preferably 4 to 7 metres per minute. For a stretch of200-400% at 4 to 7 metres per minute final speed it is necessary on theone hand to make the distance between the spinneret and the point wherethe stretch is initiated as. small as possible and, on the other hand,to establish arninimum period of 3 seconds during which the thread is.subjected to tension. The necessity for these stretching conditions mayperhaps be explained on the. theory that the high degree of stretch isonly possible and elfective when the filament to bestretched has arelatively high concentration of Xant-hate groups and that thestretching tension must be elfective while a relatively large part ofthese Xanthate. groups is. being split off. The distance between, thespinneret andthe place where the stretching is initiated may beadjusted, within the abovedescribed limits according to the gamma numberof the viscose solution at the composition. and temperature of thespinning bath. In this connection, the lower the concentration of theester groups at the point where the stretching commences, the

shorter the aforesaid distance needs to be, and vice The stretching maybe effected in any suitable man.-

ner, within the limits described above as essential to the process ofthe present lnvention. For example the filament can be stretched byfriction by means of tubular rods or between driven rolls or pairs ofrolls rotating at different peripheral speeds or by a combination ofboth systems. During the stretching the filament can move forwardpartially or wholly in the spinning bath or partially or wholly in theair.

spinneret and according tothe.

An advantageous methods.

is that in which stretching is effected during the air path. Thefilament can be drawn off vertically or horizontally through thespinning bath from the spinneret, or at any intermediate angle. Thespinnerets are of the usual construction. Where multiple hole spinneretsare employed, they are so located that the gases formed during thespinning may readily escape. The stretched filaments are spooled in anysuitable manner.

The following data give a picture of the importance of the spinning orstretching speed in accordance with the invention. Using one and thesame viscose solution and always the same bath composition a multiplefilament of 300 denier was spun with different degrees of stretch.

In the experiments indicated in the following tables, a sulphite pulpwith 89% a-cellulose content was employed. The viscose solution wasadjusted to 6.1% cellulose and 7.7 caustic soda content. Its gammanumber at the moment of spinning was 75. The cellulose regenerated fromthe viscose solution had a degree of polymerisation of 650. The spinningbath contained 20 g. sulphuric acid and g. sodium sulphate per litre.Its temperature was C. and the thread of 300/200 den. The holes of thespinneret had a diameter of 0.07 mm., the bath path was 10 cm. and thedistance between the spinneret and the place where the stretchingcommenced was 40 cm. Stretching was carried out in air between twodriven stretching rolls, the spacing of which was 120 cm. The threadswere spooled with very slight tension on rollers and then washed freefrom acid, de-sulphurised, soaped and dried. The following measurementswere made on the dried test pieces.

TABLE I Desired degree of Breaking strength, in g./den.

Elongation at rupture, in

Speed of the thread after the percent second Stretching roll, in

m'lmul strgich,

percent wet dry wet 1 Maximum possible stretch for continuous spinning.

TABLE II Speed of the thread after the second stretching roll, inm./min.

Desired degree of stretch. in percent Breaking strength in g./den.

Elongation at rupture, percent Swelling in water of 20 C. in

percent of the dry weight Test No dry wet dry wet Maximum possiblestretch for continuous spinning.

It is apparent from the results of Table I how the breaking strength andelongation at rupture of the filaments under the conditionscharacteristic of the invention increase with decreasing spinning speedwhen the stretch is constant. The result may be compared with the firstline in which the spinning speed is m./min., with which however it waspossible to obtain a maximum stretch of only 150%. In the other forms, astretch of 240% does not in any way represent the maximum. The breakingcharacteristics of the filaments may be taken as a measure of the degreeof organisation of the structure.

It is apparent from the results of Table II how, under the conditionscharacteristic of the invention, with a spinning speed of 3.14 m./min.,an increase of the stretch to the maximum permissible amount actsfavourably on the organisation of the filament structure. Thissatisfactory arrangement is apparent from the high breakingcharacteristics and also from the low swelling of the filament of TestB. The determination of the degree of swelling is carried out in thefollowing manner: 0.5 g. of thread were cut into short fibres and placedfor one hour in distilled water at 20 C. and then centrifuged at 20 C.in a centrifuge with diameter of 31 cm. for 20 minutes and at 3,000 R.P. M. Finally the water content was determined of'the' product ofconstant weight obtained by drying at 105 C. In addition, an X-raydiagram with CuK a-radiation was made on test piece B. A diagram wasobtained with a large number of clearly perceptible reflections of thefirst, second, third and fourth layer lines. The intensity and length ofthe interferences show up a very high proportion of crystallisedcellulose and a very high degree of orientation of the crystallites suchas has not been known hitherto with viscose filaments.

The invention is illustrated by the following examples which however,are not to be regarded as limiting it in any way:

Example I A sulphite pulp with 89% content of a-cellulose is mercerisedat 18 C. and then shredded at 0 C. The alkali cellulose is thenimmediately xanthogenated for 2 /2 hours with 60 parts CS2 to 100 partsa-cellulose and dissolved by stirring in four hours at a temperature of5 C. After dissolving, the gamma number is 75. The viscose solutioncontaining 6.1% a-cellulose and 7.7% NaOI-I is filtered, deaerated andspun with a gamma number of 70 and at a viscosity of 220 poises(measured at 20 C.).

A filament bundle of 10,500 den. with 7,000 individual filaments is spunfrom a spinneret, the holes of which have a diameter of 0.07 mm. Thespinning bath contains 18 g. H2804, 90 g. NazSOr and 2.5 mg. laurylpyridinium sulphate per litre. Its temperature is 20 C. and the bathpath 10 cm. The distance between the spinneret and the point at whichstretching commences is 30 cm. Stretching is carried out between drivenrolls which are arranged at a distance of 120 cm. from one another. Thedegree of stretch is 300% and the spinning speed after stretching 5m./min. The tension on the bundle with a stretch of 300% amounts to 0.78g./den. The bundle is drawn off vertically from the spinning nozzle andthen vertically towards the stretching members. The bundle produced inthis manner is relieved of tension after the stretching and iscontinuously cut to 40 mm. staple lengths in the acid condition. Thefibres are washed free from acid and salt in the usual manner,de-sulphurised, treated with an aqueous solution containing for example5 g./litre cetyl alcohol sulphate and dried. The fibres have thefollowing properties:

Breaking strength dry g./den 4.1 Breaking strengthwet g./den 3.76Elongation at rupturedry per cent 12 Elongation at rupture-wet do 14Swelling do 70 Degree of polymerisation 600 These fibres of 1.5 den.have an almost circular, nonserrated cross-section. In thephase-contrast microscope, no double layers in the cross-section are tobe observed, but instead point-like dots are revealed. The fibres can bespun into yarns by the cotton process.

Example II The preparation of the viscose solution is carried out in thesame manner as in Example 1.

The viscose solution is spun from a spinneret with 200 holes having adiameter of 0.07 mm. to form a thread of 300 den. into a spinning bathwhich contains 20 g. H2804 and 15 g. NazSO4 per litre and has atemperature of 18 C. The bath path is 3 cm. The distance between thespinneret and the point at which stretching commences is 23 cm. Thethread is drawn vertically from the spinneret and stretched horizontallybetween two driven rolls which have a spacing of cm. The stretchingamounts to 280% and the spinning speed after the stretching 4.7 m./min.The thread tension during the stretching is 0.9 g./den.

The thread is wound with light tension on to a roller and finished inthe usual manner. After the drying, it is twisted on a ring spinningmachine at turns per The percentage amount of the elastic elongation inthe dry condition to the total elongation was determined on a Scotttester, maintaining a recuperation period of one minute after eachloading:

Elastic elongation in percent of the total elongation :3 in

The dye-absorbing capacity of this thread has been compared withbleached cotton and with a commercial viscose thread of 120/80 den. with97% swelling prepared by spinning into a Muller-type bath.

Dye solution 4.32 g./lit. solar blue GLN. Bath ratio 1:800.

Dyeing temperature 60 C.

Time 16 minutes.

The dye absorption in mg. per kg. thread or fibre respectively is 530:21for the thread with 65% swelling spun in accordance with Example II,300$ 12 for bleached cotton, 530:21 for viscose thread of 120/80 den.with 97% swelling.

Despite the low swelling capacity of thread spun in accordance withExample II, the dye absorption capacity is better than with bleachedcotton and the same as with normal viscose fibre.

Example III The same viscose solution is used as in Example 1, exceptthat 0.8% titanium dioxide per kg. a-cellulose are added to it.

A bundle of 19,500 den. comprised of 1300 individual filaments of den.is spun from the spinneret, the holes of which have a diameter of 0.12mm. The spinneret is disposed in a bath which contains 60 g. H2804 andg. Na2SO4 per litre and which has an internal temperature of 22 C. Thelength of the bath is 30 cm. The bundle is drawn OE With an upwardinclination of about 30. Directly above the bath, it is stretched bypassing over and under 4 successive rods in such a manner that thebraking action takes place. It is then conducted into a stretchingdevice according to Example I. The stretching between driven rolls,which follows the stretching due to the braking action, is 150%. Thefinal speed of the thread is 5 m./niin.

The bundle is then cut into staple lengths of 100 mm. The fibres arefinished in a manner similar to that set out in Example I.

Properties:

Breaking strength-dry 2 g./ den. Breaking strength--wet 1.5 g./den.Elongation at rupture-dry 12%. Elongation at rupture-wet 15%.Cross-section Roundish with smooth edges.

Swelling 69% The relatively low swelling of this fibre indicates awellorientated structure which is remarkable for relatively coarsefibres. These fibres can be used for carpet yarns.

Example IV Linters pulp is mercerised in the usual manner in 18% NaOI-Iand squeezed out in order to produce an alkali cellulose containingabout 31% a-cellulose and 15.5% NaOH. This alkali cellulose is shreddedfor 110 minutes at 0 C. and immediately xanthated with 65 parts CS2 per100 parts a-cellulose. The xanthate is then dissolved in a beater deviceat 7 C. to form a viscose solution with 7.2% cellulose and 5.7% NaOH.The filtered and deaerated viscose arrives at the spinneret with a gammanumber of 70. It then has a viscosity of 370 poises (measured at 20 C.).A thread of 1100/480 den. is spun, using spinnerets having holes with adiameter of 0.085 mm. The spinning bath contains 20 g. H2804 and 1 g.NazSOs per litre. It has a temperature of 20 C. The thread is drawn offvertically through the bath. The first driven stretching member isdisposed in the spinning bath. The total length of the path of thethread in the bath is 45 cm., the distance between spinneret and thepoint where the 6 stretching commences is 5 cm. and the distance betweenthe two driven stretching members is 120 cm. When the speed of thestretched thread is 3 m./min., the degree of stretching is 310%.

The finished thread, twisted with turns per metre, has the followingproperties: a

Breaking strength-dry g./den 5.1 Breaking strengthwet g./den 4.5Elongation at rupture-dry per cent 7.3 Elongation at rupture-wet do..7.5

The thread can be used for tyre cords. We claim:

1. A process for the production of filaments of high organisation andhigh tensile strength having a degree of polymerisation above 300 whichcomprises extruding through spinnerets a viscose of gamma number above60, the cellulose generated from said viscose having a degree ofpolymerisation above 300, into an aqueous spinning bath at roomtemperature containing only from 10-40 g./ litre of sulphuric acid andat most 100 g./ litre of sodium sulphate, and stretching the filamentsabout 240% continuously with their formation giving a final speed of 12meters at most per minute, the filaments being maintained continuouslyunder tension.

2. A process for the production of filaments of high organisation andhigh tensile strength having a degree of polymerisation above 300 whichcomprises extruding through spinnerets a viscose of gamma number above60, the cellulose generated from said viscose having a degree ofpolymerisation above 300, into an aqueous spinning bath at roomtemperature containing only from 10-40 g./ litre of sulphuric acid andat most 100 g./ litre of sodium sulphate, and stretching the filamentscontinuously with their formation giving a final speed of 4 to 7 metersper minute, the filaments being maintained continuously under tension.

3. A process for the production of filaments of high organisation andhigh tensile strength having a degree of polymerisation above 300 whichcomprises extruding viscose at room temperature through spinnerets intoan aqueous coagulating bath, the viscose having a gamma number above 60,generating cellulose having a degree of polymerisation above 300 andhaving a cellulose content of 4 to 11% by weight and a caustic sodacontent of 3 to 12% by weight, the aqueous coagulating bath containingonly from 10-40 g./litre of sulphuric acid and at most 100 g./litre ofsodium sulphate, stretching the filaments about 240% continuously withtheir formation giving a final speed of 12 meters at most per minute,the filaments being maintained continuously under tension.

4. A process for the production of filaments of high ganisation and hightensile strength having a degree of polymerisation above 300 whichcomprises extruding through spinnerets a viscose of gamma number above60, the cellulose generated from the said viscose having a degree ofpolymerisation above 300, into an aqueous coagulating bath at roomtemperature containing only from 10 -40 g./litre of sulphuric acid andat most 100 g./litre of sodium sulphate, and stretching the filaments inthe coagulating bath about 240% continuously with their formation, thefilaments being maintained continuously under tension, the stretching ofthe filaments being initiated at a point not more than 60 cm. from thespinnerets and the final speed being not greater than 12 meters perminute.

5. A process for the production of filaments of high organisation andhigh tensile strength having a degree of polymerisation above 300 whichcomprises extruding through spinnerets a viscose of gamma number above60, the cellulose generated from said viscose having a degree ofpolymerisation above 300, into an aqueous coagulating bath at roomtemperature containing only from 10-40 g./litre of sulphuric acid and atmost 100 g./litre of sodium sulphate, and stretching the filaments about240% during a period of 3 seconds at least continuously with theirformation giving a final speed of 12 meters at most per minute, thefilaments being maintained continuously under tension.

Underwood Dec. 24, 1946 Drisch et al. Aug. 26, 1952

1. A PROCESS FOR THE PRODUCTION OF FILAMENTS OF HIGH ORGANISATION ANDHIGH TENSILE STRENGHT HAVING A DEGREE OF POLYMERISATION ABOVE 300 WHICHCOMPRISES EXTRUDING THROUGH SPINNERETS A VISCOSE OF GAMMA NUMBER ABOVE60, THE CELLULOSE GENERATED FROM SAID VISCOSE HAVING A DEGREE OFPOLYMERISATION ABOVE 300, INTO AN AQUEOUS SPINNING BATH AT ROOMTEMPERATURE CONTAINING ONLY FROM 10-40 G./LITRE OF SULPHURIC ACID AND ATMOST 100G./ LITRE OF SODIUM SULPHATE, AND STRETCHING THE FILAMENTS ABOUT240% CONTINUOUSLY WITH THEIR FORMATION GIVING A FINAL SPEED OF 12 METERSAT MOST PER MINUTE, THE FILAMENTS BEING MAINTAINED CONTINUOUSLY UNDERTENSION.